Characteristics and capabilities of navigation systems for unmanned untethered submersibles

"Navigation" is usually taken to mean the measurement of a vehicle's position within a prespecified grid. The term "geodetic navigation" is used when the grid system is global, e.g., the WGS-84 ellipsoid; "local navigation" and "positioning" are used when the grid covers a small area, e.g., a transponder net. In some cases navigation is restricted to the two horizontal coordinates (with vertical positions measured separately), while in other cases navigation refers to the measurement of all three position coordinates. Because position determination often requires the measurement of velocity or heading/pitch/roll, the sensors which perform these functions are also termed "navigation" equipment.